In a switching element such as a servo circuit or an inverter circuit, when flow of a current is forcibly turned off, a steep forward voltage is applied. Therefore, in the switching element, because power loss at the time of turning it off is large and the power loss is concentrated on a local area, the switching element itself may be broken. Particularly, when a wire for feeding a DC (Direct Current) to the switching element is long, inductive reactance of the wire becomes large, and thus the surge voltage at the time of turning off the switching element becomes higher.
Generally, the switching element is protected from the surge voltage by using a snubber circuit such as a snubber capacitor. The snubber capacitor is connected to the switching element in parallel. When the switching element is turned off, the surge voltage described above is suppressed by charging a current from the switching element into the snubber capacitor. In addition, there is a case where voltage oscillation is suppressed by connecting a resistor to the snubber capacitor in series.
As a conventional technique of protecting an element from a surge voltage without using a snubber capacitor, for example, Patent Literature 1 mentioned below discloses a technique of preventing breakage of an element due to an overcurrent (a surge current), when the overcurrent exceeding a rated value flows, by increasing a gate voltage.
Patent Literature 2 mentioned below discloses a technique of increasing an on-resistance to take over the resistance of a snubber circuit, while setting a diode used for the snubber circuit as a wide bandgap type (SiC) and operating the diode with a current density, which is 20 to 30 times denser than a current density at the time of a normal temperature operation.